The present invention relates to apparatus for dispensing fluid droplets. More particularly, it concerns an apparatus for dispensing fluid droplets on demand useful in various drop dispensing applications including ink jet printers.
Devices for the formation and dispensing of fluid droplets on demand, such as those utilized in ink jet printers, typically include a fluid-receiving chamber that is connected to a supply of fluid and to a droplet emitting nozzle or orifice. When a fluid drop is desired, the fluid is perturbed in some way to cause a predetermined volume of the fluid to issue from the nozzle in a drop-wise manner. In some devices, the fluid is exposed directly to an electric or magnetic field to cause drop-wise ejection. In other devices, the volume of the fluid chamber is momentarily reduced to force a predetermined quantity of the fluid through the nozzle. In the latter type of system, the fluid-containing chamber is defined by various wall portions with at least one of the wall portions provided with a measure of flexure. An electroactuator, typically in the form of a piezoelectric device, is connected to the flexible wall portion so that excitation of the actuator causes the connected wall to flex in such a way that the volume of the fluid chamber is momentarily reduced to force a predetermined quantity of the fluid through the nozzle in a drop-wise manner. The flexed wall thereafter returns to its initial position with replacement fluid provided from the supply reservoir.
In the past, the costs associated with the manufacture of reliable and durable drop dispensers have been relatively high because of the small physical size of the various components from which the drop dispensers are assembled and the dimensional precision required to produce devices having fluid containing chambers that will repeatedly dispense droplets of uniform volume. Many drop dispensers have been manufactured from various metals, ceramics, and glasses which materials can be formed by known micro-machining, etching, and other shaping techniques to define small volume fluid-receiving chambers which undergo a consistent volumetric reduction in response to operation of an electroactuator. As can be appreciated, however, any manufacturing process that involves multiple machining, shaping, or assembly steps to produce a reliable drop dispenser is inconsistent with inexpensive, high volume production.
Efforts have been made in the direction of forming drop dispensers from injection molded plastics. Typical design considerations in selecting a plastic include its elasticity and its ability to be molded into small precise-dimensioned components as well as the ability to be molded into elastic thin wall sections. Accordingly, a need arises for an on-demand drop dispensing device that can be efficiently and inexpensively manufactured compared to prior devices from conventional plastic resins that are well suited for injection molding.
U.S. Pat. No. 4,245,227, issued Jan. 13, 1981 is directed to an ink jet head having inner and outer cylindrical members wherein only the outer cylindrical member is a piezoelectric element in the case of a single nozzle. In the case of multiple arrays of nozzles both inner and/or outer cylindrical members may be piezoelectric members. The piezoelectric element vibrates radially when electrically excited to produce vibrations in the ink thereby ejecting the ink through the nozzles. It should be noted that the piezoelectric element is in direct contact with the ink. Such an arrangement requires that the ink be non-conductive.
U.S. Pat. No. 4,387,383, issued June 7, 1983, is directed to a multiple nozzle ink jet head which comprises an array of ink droplet producing devices arranged in a stacked sandwich-like manner. The ink jet head comprises a first cavity having a supply of ink and a second cavity which contain a plurality of droplet producing devices in stacked relationship comprising a conductive element, an annular element for containing ink in said second cavity and a transducing element such as a piezoelectric element in contact with the ink. The ink is identified as an ink of low conductivity.
U.S. Pat. No. 4,434,430, issued Feb. 28, 1984, is directed to an ink jet head wherein a piezoelectric element is bonded to a planar vibration plate formed of a synthetic resin. Activation of the piezoelectric element flexes the vibration plate normal to its plane thereby displacing ink in the adjacent chamber. In an alternative embodiment, the piezoelectric element is formed of a high molecular weight piezoelectric material which can double as the vibration plate.